Add Toffoli (#323)

Author: mpharrigan

dev_tools/autogenerate-bloqs-notebooks.py

@@ -55,6 +55,7 @@
 import qualtran.bloqs.basic_gates.rotation_test
 import qualtran.bloqs.basic_gates.swap_test
 import qualtran.bloqs.basic_gates.t_gate_test
+import qualtran.bloqs.basic_gates.toffoli_test
 import qualtran.bloqs.basic_gates.x_basis_test
 import qualtran.bloqs.basic_gates.z_basis_test
 import qualtran.bloqs.factoring.mod_exp
@@ -87,6 +88,7 @@
             BloqNbSpec(qualtran.bloqs.basic_gates.z_basis_test._make_zero_state),
             BloqNbSpec(qualtran.bloqs.basic_gates.t_gate_test._make_t_gate),
             BloqNbSpec(qualtran.bloqs.basic_gates.rotation_test._make_Rz),
+            BloqNbSpec(qualtran.bloqs.basic_gates.toffoli_test._make_Toffoli),
         ],
         directory=f'{SOURCE_DIR}/bloqs',
     ),

qualtran/bloqs/basic_gates.ipynb

@@ -13,7 +13,9 @@
     "\n",
     "The bloqs in this module encode gates you'd expect to find in any quantum computing\n",
     "framework. It includes single-qubit unitary gates like rotations, bit- and phase-flip;\n",
-    "basic multi-qubit unitary gates; and states and effects in the Pauli basis."
+    "basic multi-qubit unitary gates; states and effects in the Pauli basis; and non-Clifford\n",
+    "gates `TGate` and `Toffoli` which are commonly counted to estimate algorithm resource\n",
+    "requirements."
    ]
   },
   {
@@ -373,6 +375,53 @@
     "psi = circuit.final_state_vector()\n",
     "psi * np.sqrt(2)"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "30a5458b",
+   "metadata": {
+    "cq.autogen": "_make_Toffoli.md"
+   },
+   "source": [
+    "## `Toffoli`\n",
+    "The Toffoli gate.\n",
+    "\n",
+    "This will flip the target bit if both controls are active. It can be thought of as\n",
+    "a reversible AND gate.\n",
+    "\n",
+    "Like `TGate`, this is a common compilation target. The Clifford+Toffoli gateset is\n",
+    "universal.\n",
+    "\n",
+    "#### References\n",
+    "[Novel constructions for the fault-tolerant Toffoli gate](https://arxiv.org/abs/1212.5069). Cody Jones. 2012. Provides a decomposition into 4 `TGate`.\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "020ce731",
+   "metadata": {
+    "cq.autogen": "_make_Toffoli.py"
+   },
+   "outputs": [],
+   "source": [
+    "from qualtran.bloqs.basic_gates import Toffoli\n",
+    "\n",
+    "bloq = Toffoli()\n",
+    "show_bloq(bloq)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "0aca6c53",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from qualtran.resource_counting import get_bloq_counts_graph, GraphvizCounts\n",
+    "g, sigma = get_bloq_counts_graph(bloq)\n",
+    "GraphvizCounts(g).get_svg()"
+   ]
   }
  ],
  "metadata": {

qualtran/bloqs/basic_gates/__init__.py

@@ -16,12 +16,15 @@
 
 The bloqs in this module encode gates you'd expect to find in any quantum computing
 framework. It includes single-qubit unitary gates like rotations, bit- and phase-flip;
-basic multi-qubit unitary gates; and states and effects in the Pauli basis.
+basic multi-qubit unitary gates; states and effects in the Pauli basis; and non-Clifford
+gates `TGate` and `Toffoli` which are commonly counted to estimate algorithm resource
+requirements.
 """
 
 from .cnot import CNOT
 from .rotation import Rx, Ry, Rz
 from .swap import CSwap, TwoBitCSwap, TwoBitSwap
 from .t_gate import TGate
+from .toffoli import Toffoli
 from .x_basis import MinusEffect, MinusState, PlusEffect, PlusState, XGate
 from .z_basis import IntEffect, IntState, OneEffect, OneState, ZeroEffect, ZeroState, ZGate

qualtran/bloqs/basic_gates/toffoli.py

@@ -0,0 +1,68 @@
+#  Copyright 2023 Google LLC
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+from functools import cached_property
+from typing import Dict, Optional, Set, Tuple, TYPE_CHECKING, Union
+
+from attrs import frozen
+
+from qualtran import Bloq, Register, Signature
+from qualtran.bloqs.basic_gates import TGate
+
+if TYPE_CHECKING:
+    import cirq
+
+    from qualtran.cirq_interop import CirqQuregT
+    from qualtran.resource_counting import BloqCountT, SympySymbolAllocator
+    from qualtran.simulation.classical_sim import ClassicalValT
+
+
+@frozen
+class Toffoli(Bloq):
+    """The Toffoli gate.
+
+    This will flip the target bit if both controls are active. It can be thought of as
+    a reversible AND gate.
+
+    Like `TGate`, this is a common compilation target. The Clifford+Toffoli gateset is
+    universal.
+
+    References:
+        [Novel constructions for the fault-tolerant Toffoli gate](https://arxiv.org/abs/1212.5069).
+        Cody Jones. 2012. Provides a decomposition into 4 `TGate`.
+    """
+
+    @cached_property
+    def signature(self) -> Signature:
+        return Signature([Register('ctrl', 1, shape=(2,)), Register('target', 1)])
+
+    def bloq_counts(self, ssa: Optional['SympySymbolAllocator'] = None) -> Set['BloqCountT']:
+        return {(4, TGate())}
+
+    def on_classical_vals(
+        self, ctrl: 'ClassicalValT', target: 'ClassicalValT'
+    ) -> Dict[str, 'ClassicalValT']:
+        assert target in [0, 1]
+        if ctrl[0] == 1 and ctrl[1] == 1:
+            target = (target + 1) % 2
+
+        return {'ctrl': ctrl, 'target': target}
+
+    def as_cirq_op(
+        self, qubit_manager: 'cirq.QubitManager', ctrl: 'CirqQuregT', target: 'CirqQuregT'
+    ) -> Tuple[Union['cirq.Operation', None], Dict[str, 'CirqQuregT']]:
+        import cirq
+
+        (trg,) = target
+        return cirq.CCNOT(*ctrl[:, 0], trg), {'ctrl': ctrl, 'target': target}

qualtran/bloqs/basic_gates/toffoli_test.py

@@ -0,0 +1,78 @@
+#  Copyright 2023 Google LLC
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+import itertools
+
+import cirq
+
+from qualtran import BloqBuilder
+from qualtran.bloqs.basic_gates import TGate, Toffoli, ZeroState
+from qualtran.resource_counting import get_bloq_counts_graph
+
+
+def _make_Toffoli():
+    from qualtran.bloqs.basic_gates import Toffoli
+
+    return Toffoli()
+
+
+def test_toffoli_t_count():
+    counts = Toffoli().bloq_counts()
+    assert counts == {(4, TGate())}
+
+    _, sigma = get_bloq_counts_graph(Toffoli())
+    assert sigma == {TGate(): 4}
+
+
+def test_toffoli_cirq():
+    bb = BloqBuilder()
+    c0, c1, trg = [bb.add(ZeroState()) for _ in range(3)]
+    ctrl, target = bb.add(Toffoli(), ctrl=[c0, c1], target=trg)
+    ctrl, target = bb.add(Toffoli(), ctrl=ctrl, target=target)
+    cbloq = bb.finalize(q0=ctrl[0], q1=ctrl[1], q2=target)
+
+    circuit, qubits = cbloq.to_cirq_circuit()
+    cirq.testing.assert_has_diagram(
+        circuit,
+        """\
+_c(0): ───@───@───
+          │   │
+_c(1): ───@───@───
+          │   │
+_c(2): ───X───X───""",
+    )
+
+
+def test_classical_sim():
+    tof = Toffoli()
+
+    for c0, c1 in itertools.product([0, 1], repeat=2):
+        ctrl, target = tof.call_classically(ctrl=[c0, c1], target=0)
+        assert ctrl.tolist() == [c0, c1]
+        if c0 == 1 and c1 == 1:
+            assert target == 1
+        else:
+            assert target == 0
+
+
+def test_classical_sim_2():
+    bb = BloqBuilder()
+    c0, c1, trg = [bb.add(ZeroState()) for _ in range(3)]
+    ctrl, target = bb.add(Toffoli(), ctrl=[c0, c1], target=trg)
+    ctrl, target = bb.add(Toffoli(), ctrl=ctrl, target=target)
+    cbloq = bb.finalize(q0=ctrl[0], q1=ctrl[1], q2=target)
+
+    b0, b1, b2 = cbloq.call_classically()
+    assert b0 == 0
+    assert b1 == 0
+    assert b2 == 0